Multichannel data

Figure 13. (a) Experimental approach for simultaneous collection of potential and current noise, (b) Schematic for remotely controlled impedance and noise multichannel data collection system. (Reprinted from F. Mansfield, C. Chen, C. C. Lee, and H. Xiao, The Effect of Asymmetric Electrodes on the Analysis of Electrochemical Impedance and Noise Data, Corros. Sci. 38 (3) 497, Fig. 1. Copyright 1996 with permission of Elsevier Science.)...

Extracting analyte concentrations from spectra of complex systems containing multiple analyte contributions with overlapping spectral features requires more information than is obtainable in a single wavelength measurement. Multivariate techniques take the full-range spectrum into account and exploit the multichannel (data at many wavelengths) nature of spectroscopic data to extract concentration information from analytes.19 20... 

For systems producing multichannel data, such as GCxGC-MS, the baseline can be estimated in each channel using the same method. Baseline correction for centroided multispectral data is difficult because the centroiding process removes many (or all) of the background values. Therefore, baseline correction should be performed before or at the same time as spectral centroiding (but, unfortunately, that is not always done). 

Rule-based methods follow another approach for chemical identification with multichannel data. Experienced analytical chemists often use rules to deduce chemical identity [39,40]. In a computer-based system, rules express the reasons or criteria for chemical identification. Welthagen et al. [41] used a rule-based... 

The corrosion probe used in this example is illustrated in Figs. 5.32 and 5.33. A retractable probe with flexible depth was selected, in order to mount the sensor surface flush with the internal scrubber wall surface. The close spacing of the carbon steel sensor elements was designed to work with a discontinuous thin surface electrolyte film. This corrosion sensor was connected to a handheld multichannel data recorder by shielded multistrand cabling Fig. 5.34. As the ducting of the gas scrubbing tower was heavily insulated, no special precautions were taken to cool the corrosion sensor s surface. 

What is required are techniques to reliably analyze complex multichannel data. Recently, processing methods developed for multiband satellite images have successfully been applied also to the analysis of microscope images [8,9]. By this linear unmixing of multichannel data, clean representations of the fluorophores in the sample can be created and be quantitatively analyzed. 

FIGURE 7.4 Profiles of different masses are built up using a multichannel data acquisition... 

Stored and counted by a multichannel analyzer. This multichannel data acquisition system typically has 20 channels per mass and as the electrical pulses are counted in each channel, a profile of the mass is built up over the 20 channels, corresponding to the spectral peak of Cu. In a multielement run, repeated scans are made over the entire suite of analyte masses, as opposed to just one mass represented in this example. The principles of multielement peak acquisition are shown in Figure 12.3. In this example, signal pulses for two masses are continually collected as the quadrupole is swept across the mass spectrum, shown by sweeps 1-3. After a fixed number of sweeps (determined by the user), the total number of signal pulses in each channel is obtained, resulting in the final spectral peak. ... 

FIG U RE 7.4 Profiles of different masses are built up using a multichannel data acquisition system. (Courtesy of PerkinElmer, Inc., 2003-2012. All rights reserved. With permission.)... 

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